An element made of a wide band gap semiconductor as typified by GaN, SiC and so on has excellent characteristics such as high-speed switching and a low ON resistance value as compared to an element made of a silicon semiconductor. On the other hand, the element made of a wide band gap semiconductor exhibits a normally-on characteristic in which a drain current flows therethrough even when a gate voltage is 0V, or a normally-off characteristic with a low threshold voltage of about 2V. Thus, the gate voltage needs to be driven to a negative voltage in order to ensure that this element is turned off.
Japanese Patent Laying-Open No. 2007-288992 (PTD 1) describes a semiconductor circuit for switching elements having a normally-on characteristic or switching elements having a normally-off characteristic with a low threshold voltage.
In PTD 1, a power supply circuit for generating a negative voltage to be supplied to a high side (high-voltage side) switching element and a power supply circuit for generating a negative voltage to be supplied to a low side (low-voltage side) switching element are provided, with a high-voltage side of the high side power supply circuit being connected to a positive terminal of a high-voltage power supply. Also provided is a control capacitor having one electrode connected to a low-voltage (negative voltage) side of the high side power supply circuit. A control circuit for controlling on/off of the switching elements is provided with an operation power supply from the control capacitor which is charged when the switching elements are on. As an example of the power supply circuit, a configuration is described in which a current flows to a capacitor through another switching element, and a Zener diode is connected in parallel to the capacitor to form a negative voltage power supply.
Japanese Patent Laying-Open No. 2006-314154 (PTD 2) discloses a power converter for supplying a negative voltage to a normally-on switching element on a high side by using a constant voltage diode (Zener diode).
International Rectifier Japan Application Note AN-1120 (NPD 1) describes a buffer circuit driven with a negative gate-bias voltage.